1. Field of the Invention
The present invention relates to a system and method of closed loop ramping control of fusing temperature and optimization of the time to make a first copy. More particularly, the present invention relates to a system and method of controlling a printer so that print media arrives at the fuser just after the fuser achieves a desired target temperature.
2. Description of the Prior Art
The amount of time it takes for a job, sent from a host device to be printed, and to reach the printer's output bin is known as first copy time, and is an important feature to users of the printer. In conventional printers, the gate for first copy time, in electrophotographic printing, typically has been the amount of time it takes to warm the cold fuser to the temperature needed for fusing the image onto the print media. Such warmup time has been dramatically reduced by the use of a ceramic heating element within the fuser. However, the physical properties of the ceramic heating element are such that when it heats too quickly, the ceramic heating element is susceptible to cracking damage.
To achieve the best first copy time, the fuser must be heated as fast as possible without damaging the ceramic heating element. It is desirable to ramp up the temperature at a consistent rate, independent of line voltage, line frequency, and target temperature, in order to allow the control algorithm to predict the point in time when the fuser will reach the target temperature. Being able to predict the point at which the target temperature is achieved allows the control algorithm to begin feeding the print media at a point in time so that the print media reaches the fuser immediately after the fuser has achieved the desired target or steady state temperature. As a result, the application of any unnecessary energy to the fuser is prevented while the fuser is waiting for the print media to arrive.
Providing a consistent rate of temperature rise can be challenging due to the worldwide variations in line voltage and frequency. Line voltage for 110-volt machines can vary anywhere from 90VRMS to 139VRMS, for example, and the line frequency can be either 50 Hz or 60 HZ. Therefore, an open loop (no feedback control) ramping algorithm that provides a desirable rate of rise for one extreme line voltage condition will likely produce an undesirable rate of rise at the opposite extreme line voltage condition. Here open loop refers to a method of applying an input to the system (heat) and not using the output as a feedback for adjusting the level of the input.
In addition to line voltage extremes, open loop algorithms regulating heat to the fuser by adjusting the heat on time via AC half cycles are sensitive to line frequency. These routines must take into account that a 50 Hz half cycle produces a longer "on" time than a 60 Hz half cycle (10 ms and 8.33 ms, respectively). As a result, more power will be delivered to the fuser at 50 Hz for the same half cycle setting. Consequently, AC half cycle control algorithms must detect line frequency and perform some sort of line voltage measurement in order to find a suitable open loop ramping solution. If the line voltage detection is performed with hardware, there is a dollar cost involved. A software measurement of line voltage during ramp up would have to be conservative to prevent damage at high line voltage conditions, which would be detrimental to the first copy time of the printer. Therefore, a ramp without feedback, an open loop ramping algorithm, lacks the robustness to deliver a consistent rate of temperature rise in the fuser heater.
Similarly, a closed loop ramping algorithm alone, which tries to lock in on the desired, or steady state, temperature via feedback control, has deficiencies. In a closed loop control system the actual (temperature) is compared to the desired output of the system and is used as feedback to adjust the input accordingly. The rate of rise to the steady state temperature is determined by the gain constants in the control equation, which could be satisfactory for one line condition but not for another. However, one could use such a closed loop control method to track discrete temperature along an arc that leads up to the steady state temperature, rather than directly tracking the final steady state temperature. In this manner, the ramping arc follows in a piece-wise linear fashion, and the control algorithm can "snap to" the discrete target temperatures, thereby producing the desired consistent rate of rise. Achieving a robust, consistent fuser temperature ramp up will produce a consistent first copy time that is independent of the line voltage and the line frequency.
From the foregoing, it is an object of the present invention to provide a system and method of closed loop ramping control of fusing temperature such that the first copy time is minimized, yet the damage to the fuser from heating too quickly is minimized.
Another object of the present invention is to provide a system and method of closed loop ramping control of fusing temperature in which the best first copy time is achieved by heating the fuser as fast as possible without damaging the ceramic heating element. Heat rates less than 125 degrees Celsius/second have been found to be acceptable, but heating rates greater than 170 degrees Celsius/second will cause ceramic failure, i.e. cracking.
Yet another object of the present invention is to provide a system and method of closed loop ramping control of fusing temperature in which the temperature is ramped up at a consistent rate, independent of line voltage, line frequency, and target temperature, in order to allow the control algorithm to predict the point in time when the fuser will reach the target temperature.
Still another object of the present invention is to provide a system and method of closed loop ramping control of fusing temperature so that print media is fed so that the print media reaches the fuser immediately after the fuser has achieved the desired target or steady state temperature.
Another object of the present invention is to provide a system and method of closed loop ramping control of fusing temperature that tracks discrete temperature along an arc track leading up to a steady state temperature, instead of directly tracking a final steady state temperature, so that the ramping arc follows in a piece-wise linear fashion, thereby producing the desired consistent rate of rise, and thereby achieving a robust, consistent fuser temperature ramp up which will produce a consistent first copy time that is independent of the line voltage and the line frequency.